Physics: Chapter 2

What is the net force when a pair of 5-N forces simultaneously act in the same direction on an object?

10 N

Consider a book that weighs 15 N at rest on a flat table. How many newtons of support force does the table exert on the book?

15 newtons up

If you pull horizontally on a crate with a force of 200 N, it slides across the floor in dynamic equilibrium. How much friction is acting on the crate?

200 N

How much support force acts on a 200-N girl standing on a weighing scale?

200 N

The resultant of a 40-N force at right angles to a 30-N force is

50 N.

Why do we say that force is a vector quantity?

A force has a magnitude and a direction.

What does it mean to say something is in mechanical equilibrium?

An object in mechanical equilibrium experiences a zero net force.

What are the units for force?

Force can be expressed in newtons or pounds.

A bird sitting in a tree is traveling at 30 km/s relative to the faraway Sun. When the bird drops to the ground below, does it still move at 30 km/s, or does this speed become zero?

It continues to move at 30km/s relative to the Sun, but it has a speed of 0 km/s relative to the ground.

What type of path does a moving object follow in the absence of a force?

It continues to move in a straight line at a constant speed.

How does Newton's first law of motion relate to Galileo's concept of inertia?

Newton refined Galileo's concept of inertia and made it his first law of motion.

Which of Newton's laws does the equilibrium rule illustrate?

Newton's first law

What relationship between the Sun and Earth did Copernicus formulate?

The Earth revolved in a circle about the Sun.

According to the parallelogram rule, what quantity is represented by the diagonal of a constructed parallelogram?

The diagonal is the resultant, or sum, of two vectors.

If you push on a crate with a horizontal force of 100 N and it slides at constant velocity, what is the magnitude and direction of the frictional force acting on the crate?

The frictional force on the crate is 100 N opposite the direction of motion.

What is the net force on a cart that is pulled to the right with 100 pounds of force and to the left with 30 pounds of force?

The net force is 70 pounds to the right.

What is the net force on a bag pulled down by gravity with a force of 18 newtons and pulled upward by a rope with a force of 18 newtons?

The net force is zero newtons.

What is the net force on an object in either static or dynamic equilibrium?

The net force is zero.

What is the resultant of a pair of one pound forces at right angles to each other?

The resultant is a force of 1.41 pounds in a direction bisecting the 90-degree angle between the two vectors.

What concept was not understood in the 16th century when people couldn't conceive of a moving Earth?

They did not understand inertia.

Stand next to a wall that travels at 30 km/s relative to the Sun. With your feet on the ground, you also travel at the same 30 km/s. Do you maintain this speed when your feet leave the ground? What concept supports your answer?

When you jump, you continue to move at 30 km/s due to your inertia.

A bowling ball at rest is in equilibrium. Is the ball in equilibrium when it moves at constant speed in a straight-line path?

Yes, the bowling ball is in equilibrium because ΣF = 0.

When you stand at rest on a bathroom scale, how does your weight compare with the support force from the scale?

Your weight is equal in magnitude and opposite in direction to the support force from the scale.

The amount of force needed to sustain motion of a rock in outer space is

a force less than its weight if friction is absent. a force equal to its weight. ****none of these****

Newton said that something was needed to change the motion of an object. A clear reading of his first law tells us that what is needed is ______.

a non-zero net force

vector quantity

a quantity that has both magnitude and direction, such as force

scala quantity

a quantity that has magnitude but not direction, such as mass and volume

vector

an arrow drawn to scale used to represent a vector quantity

If you toss a coin straight upward while in a train moving at constant velocity, the coin will land

as if you were at rest.

A hockey puck is set in motion across a frozen pond. If ice friction and air resistance are neglected, the force required to keep the puck sliding at constant velocity is

equal to its weight. equal to its weight divided by its mass. equal to its mass times its weight. ****none of the above****

newton's first law of motion ( the law of inertia)

every object continues in a state of rest of uniform speed in a straight line unless acted on by a nonzero net force

Whirl a rock at the end of a string and it follows a circular path. If the string breaks, the tendency of the rock is to

follow a straight-line path.

equilibrium rule

for any object or system of objects in equilibrium, the sum of the forces acting equals zero.

When Nellie Newton hangs by the ends of a rope draped over a large pulley, the tension in each supporting vertical strand is

half her weight

force

in the simplest sense, a push or a pull

When you flick a card from beneath a coin that hardly moves, you're illustrating

inertia.

Galileo taught us that if you roll a ball along a level surface it will

keep rolling if friction is absent.

An object in mechanical equilibrium is an object

moving with constant velocity. having no changes in velocity. at rest. ****all of the above****

The force that causes Earth to orbit the Sun is due to gravity, while the force needed to keep Earth moving as it circles the Sun is

no force at all.

A force of gravity pulls downward on a book on a table. What force prevents the book from accelerating downward?

normal force

A hockey puck sliding across the ice finally comes to rest because

of friction.

Inertia is defined as a

property of matter.

Monkey Mo hangs from the middle of a horizontal rope. Tension in the rope is greatest if the rope

sags very little.

When no forces act on moving objects their paths are normally

straight lines.

resultant

the net result of a combination of two or more vectors

inertia

the property of things to resist changes in motion

mechanical equilibrium

the state of an object or system of objects for which there are no changes in motion. In accord with Newton's first law, if an object is at rest, the state of rest persists. If an object is moving, its motion continues without change

net force

the vector drawn to scale used to represent a vector quantity

Earth continually moves about 30 km/s through space, which means the wall you stand next to also is moving at 30 km/s. When you jump vertically the wall doesn't slam into you because

you're moving horizontally just as fast as the wall.

While you are standing in the aisle of a bus, the driver suddenly makes a left turn. You lurch to the right due to

your tendency to keep moving forward.

The net force on any object in equilibrium is

zero.

State the equilibrium rule for forces in symbolic notation

ΣF = 0